Conventional castable polyurethane elastomers have been used in various industries for over fifty years. Polyurethane is generally the product of a reaction between a polyurethane prepolymer and a curing agent. The polyurethane prepolymer is typically made by combining a polyol with a diisocyanate, such as toluene diisocyanate (TPI). The curing agent is often either a diamine or a short chain dial. In many instances, a catalyst is added to the polyurethane prepolymer and curing agent to promote the reaction that forms the polyurethane.
Polyurethane elastomers have been employed in the construction of industrial rollers, such as paper mill rolls. Polyurethane elastomers have been selected for use in paper mill rolls because they exhibit advantages in load bearing capability and abrasion resistance over natural and synthetic rubber materials; this is particularly important for paper mill rolls, where they experience high dynamic loads. In some papermaking machines, the rolls are also exposed to high moisture and elevated temperatures. These conditions can cause melting or debonding of the polyurethane, thereby rendering it unsuitable for use.
Some researchers have attempted to address these problems by employing polytetramethylene ether glycol (PTMEG) as the polyol of the prepolymer. For example, International Publication No. WO94/137 22 to Rosenburg, et al., discusses a low free toluene diisocyanate (TDI) prepolymer system modified with aliphatic diisocyanate methylene bis(4-cyclohexyl isocyanate) to reduce the propensity to crack during processing. To produce high performance polyurethane elastomers with low heat build-up, the modified TDI prepolymers are cured with aromatic diamine 4,4'-methylene-bis-(3-chloro-2,6-diethyl aniline) (M-CDEA). However, these elastomer systems exhibit inferior water diffusion and water vapor transmission characteristics when compared to conventional PTMEG polyether-based systems at the same hardness.